Process for the preparation of a polythiol

Abstract

The present invention relates to a process for the preparation of polythiols comprising preparing a mercaptanization reaction medium, simultaneously carrying out a radical mercaptanization reaction of said at least one polyene and an acid-catalyzed mercaptanization reaction of said at least one polyene, and recovering a mixture comprising at least two polythiols. The present invention also relates to a mixture of polythiols obtained according to said process and to the use of said mixture of polythiols.

Description

[0001] The present invention relates to the preparation of polythiols, more particularly to a process for preparing polythiols having a controlled content of their primary, secondary and tertiary thiols.

[0002] According to the primary, secondary or tertiary polythiol desired to be prepared, various methods exist for obtaining polythiols.

[0003] Among the processes for preparing polythiols, it is notably known to prepare polythiols by a radical route. This process mainly leads to obtaining primary polythiols, more generally, to the addition of -SH groups to the least substituted sp 2 carbon atoms and / or to the formation of the most stable groups on the sp 2 carbon atoms. A process for preparing a polythiol composition comprising primary thiols from a hydrocarbon compound having at least two double bonds, a phosphite compound and hydrogen sulfide is for example disclosed in application US 2012 / 0035291.

[0004] It is also known to prepare polythiols by acid catalysis; said catalysis allows the formation of polythiols mainly comprising secondary and / or tertiary thiols, more generally, to the addition of -SH groups on the most substituted and / or leading to the formation of the most stable carbon cations on the sp 2 carbon atoms. Thus, applications FR 2844794 and FR 2531426 describe a process for preparing thiols by catalysis from olefins and hydrogen sulfide acid.

[0005] However, not all these techniques allow obtaining polythiols having a high content of thiols and whose regioselectivity of the thiol groups is controlled.

[0006] Thus, there remains a need for a process allowing obtaining polythiols whose content of primary, secondary and tertiary thiols is controlled.

[0007] The Applicant found that this aim can be achieved by the process described in the following description.

[0008] According to a first aspect, the present invention relates to a process for preparing polythiols, the process comprising at least the following steps:

[0009] a / preparing a sulfhydration medium comprising contacting:

[0010] - at least one polyene;

[0011] - at least one radical initiator;

[0012] - at least one acid catalyst;

[0013] - at least one mercapto-donor compound;

[0014] - optionally, at least one solvent;

[0015] b / said at least one radical mercapto-functionalization of the polyene and said at least one acid-catalyzed mercapto-functionalization of the polyene are carried out simultaneously;

[0016] c / a mixture comprising at least two polysulfides is recovered.

[0017] The process according to the application makes it possible to obtain a mixture comprising at least two polysulfides, the at least two polysulfides obtained generally being polysulfides of the same molecular weight, but the thiol functions of which are borne by different carbon atoms. For the purposes of the application, the process thus allows a mixture of positional isomers of polysulfides to be obtained. Advantageously, very particularly preferably, the process of the application leads to the formation of polysulfides which no longer contain double bonds, that is to say, all the double bonds of the starting polyene are sulfurized with the process of the application.

[0018] "Polysulfide" is understood to mean a compound comprising at least two thiol functions (-SH).

[0019] The term "controlled" is understood to mean that a polysulfide is obtained whose regioselectivity of the thiol functions is different from that obtained by carrying out the radical mercapto-functionalization alone or the acid-catalyzed hydrogen sulfuration alone.

[0020] Indeed, when the radical mercapto-functionalization is carried out alone, the least substituted polysulfides are mainly obtained, that is to say, the majority of the thiol functions are attached to the least substituted and / or to carbon atoms from which the most stable radicals are formed.

[0021] As regards the acid-catalyzed mercapto-functionalization, when the latter is carried out alone, the most substituted polysulfides are mainly obtained, that is to say, the majority of the thiol functions are attached to the most substituted and / or to carbon atoms from which the most stable carbocations are formed.

[0022] According to the process of the application, by allowing the two reactions mentioned above to be carried out simultaneously, it is possible to control, that is to say, to modify even reverse, this regioselectivity. Indeed, the polysulfides obtained in a minority after the radical mercapto-functionalization alone or after the acid-catalyzed hydrogen sulfuration alone become the polysulfides which are mainly obtained by the process according to the application.

[0023] "Polyene" is understood to mean a compound whose hydrocarbon chain comprises at least two unsaturations in the form of double bonds ("olefinic" unsaturations). This hydrocarbon chain can be linear or cyclic, saturated or unsaturated, can optionally comprise one or more heteroatoms, and can be interrupted or substituted by one or more aromatic groups. The polyenes in the sense of the application generally have a molecular weight of between 40 g.mol -1 and 1500 g.mol -1 , preferably between 40 g.mol -1 and 1000 g.mol-1 more preferably 40 g.mol -1 up to 500 g.mol -1 of molar mass, including the extreme values.

[0024] According to one embodiment of the application, the polyene is a hydrocarbon compound comprising from 2 to 20 double bonds, preferably from 2 to 16 double bonds, more preferably from 2 to 10 double bonds, in particular from 2 to 8 double bonds, typically from 2 to 4 double bonds, including the extreme values.

[0025] According to one very particularly preferred embodiment of the application, the polyene is a hydrocarbon compound comprising 2 double bonds, preferably 3 double bonds, more particularly 4 double bonds.

[0026] Preferably, the double bonds of the polyene are not included in a ring. More preferably, at least 2 double bonds of the polyene are not delocalized to form an aromatic ring.

[0027] According to one embodiment of the application, the polyene comprises one or more heteroatoms chosen from columns 15, 16 and 17 of the periodic table of the elements, more particularly heteroatoms chosen from sulfur, nitrogen, oxygen and phosphorus.

[0028] According to one preferred embodiment, the polyene is chosen from terpenes and derivatives thereof comprising at least two double bonds, such as isoprene, limonene, myrcene, phellandrene, terpinene, ocimene, terpinolene, geraniol, citral, retinol, beta-carotene, farnesene, selinene, cardinene, farnesol, humulene, linalool and nerolidol.

[0029] According to another preferred embodiment, the polyene is a compound comprising one or more heteroatoms, for example, triallyl isocyanurate and derivatives thereof.

[0030] The radical initiator according to the application can be any radical initiator known to the person skilled in the art. The radical initiator can be chosen from thermal initiators (such as heating), photochemical initiators (such as radiation, more particularly ultraviolet radiation), and organic or inorganic compounds that generate radicals, etc., as well as combinations of two or more of them. In the case where the radical initiator is an organic or inorganic compound, it can be a peroxide, such as hydrogen peroxide, sodium peroxide, potassium peroxide, a tertiary alkyl hydroperoxide, a tertiary alkyl peroxide, a tertiary alkyl peracid ester, a cumene hydroperoxide, or the radical initiator can also be azobisisobutyronitrile, 2,2-dimethoxy-1,2-diphenylethan-1 -one, the radical initiator can be used alone or as a combination of two or more of them. Alkyl phosphites or xanthene derivatives, such as those described in patent application FR 2 501 679, can also be used.

[0031] According to a preferred embodiment of the application, the initiation of radicals is obtained by heating and / or by light radiation (for example ultraviolet light).

[0032] According to another preferred embodiment of the application, the radical initiator comprises 2,2-dimethoxy-1,2-diphenylethan-1 -one, for example sold under the name Irgacure® 651, optionally mixed with other radical initiators as described for example in applications US 4,443,310 A and US 4,233,128 A.

[0033] When it is necessary or desired, the reaction medium can be heated at a temperature between 25°C and 150°C, preferably between 25°C and 100°C, in particular between 25°C and 70°C.

[0034] When the irradiation that initiates comprises the reaction medium, it can be carried out for example by direct or indirect photolysis, preferably direct photolysis, in the wavelength range extending from about 180 nm to 600 nm, preferably by ultraviolet radiation and radiation for example with a wavelength between 180 nm and 400 nm.

[0035] The acid catalyst is chosen from all the acid catalysts known to the person skilled in the art for carrying out acid catalysis, homogeneous or heterogeneous, and can for example be chosen from Lewis acids, acidic resins such as sulfonated resins (for example styrene-divinylbenzene copolymers as described for example in application FR 2 531 426) and catalytic compositions comprising at least one metal salt, in which the metal is chosen from metals belonging to groups 8, 9 and 10 of the periodic table of the elements (as described for example in application FR 2 844 794), used alone or as a combination of two or more thereof.

[0036] According to one embodiment of the application, the acid catalyst is a sulfonated resin of the styrene-divinylbenzene copolymer type, for example Amberlyst® 15 resin.

[0037] The mercapto donor compound can be any type known to the person skilled in the art that is capable of generating a mercapto (-SH) group under the reaction conditions, i.e. the addition of a -SH group and a hydrogen atom to the sp 2 Carbon of the polyenes. The mercapto donor compound can be chosen from hydrogen sulfide, thio carboxylic acids, for example thioacetic acid, and precursors of these compounds, used alone or as a combination of two or more thereof. Among the precursors of mercapto donor compounds, mention can be made for example of dialkyldisulfides and dialkyldisulfides, for example dimethyl disulfide (DMDS), diethyl disulfide (DEDS), dipropyl disulfide (DPDS), dibutyl disulfide (DBDS), as well as higher homologues, and mixtures of them in any proportion, as can be found in DSO (or "Disulfid Oil" in English).

[0038] According to a preferred embodiment, the process according to the present application is carried out in the absence of a solvent.

[0039] According to another preferred embodiment, the process according to the present application is carried out in the presence of a solvent. The amount of solvent used can vary within a wide range and can be easily assessed and adjusted by the person skilled in the art depending on the reagents used, the reaction temperature and other reaction parameters.

[0040] When a solvent is used, this solvent can be any type known to the person skilled in the art, in particular a solvent selected from water and organic compounds and mixtures thereof in any ratio. The organic compounds which can be used as solvents are generally selected from aliphatic hydrocarbon compounds, aromatic hydrocarbon compounds optionally containing one or more heteroatoms selected from oxygen, sulfur, nitrogen and halogen.

[0041] Thus, the solvent can be selected from hydrocarbons, ketones, alcohols, ethers, esters, sulfoxides (e.g. dimethylsulfoxide), sulfolanes, nitriles (e.g. acetonitrile), used alone or as a combination of two or more thereof.

[0042] According to one embodiment of the present application, the solvent is an aliphatic hydrocarbon compound, wherein the hydrocarbon chain is linear or cyclic, branched or unbranched and contains 3 to 20 carbon atoms, preferably 4 to 15 carbon atoms. In particular 5 to 10 carbon atoms.

[0043] According to another embodiment of the present application, the solvent is an aromatic hydrocarbon compound containing 6 to 30 carbon atoms, preferably 6 to 20 carbon atoms, in particular 6 to 10 carbon atoms. The aromatic hydrocarbon compound can for example be selected from benzene, toluene, xylene (o-xylene, p-xylene, m-xylene) and ethylbenzene, used alone or as a combination of two or more thereof.

[0044] According to one embodiment of the present application, the solvent is a ketone containing 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms, in particular 2 to 6 carbon atoms. The ketone can be selected from acetone, ethyl methyl ketone and methyl isobutyl ketone, used alone or as a combination of two or more thereof.

[0045] According to one embodiment of the present application, the solvent is an alcohol containing 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms. The alcohol is selected from methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, benzyl alcohol, phenol, cyclohexanol, used alone or as a combination of two or more thereof.

[0046] According to one embodiment of the application, the solvent is an ether comprising from 2 to 20 carbon atoms, preferably from 2 to 10 carbon atoms. The ether can be cyclic or not and can be chosen from dimethyl ether, diethyl ether, methyl ethyl ether, glycol monoether, glycol diether, furan, dihydrofuran, tetrahydrofuran, pyran, dihydropyran, tetrahydropyran, 1,2-dioxane, 1,3-dioxane, 1,4-dioxane.

[0047] The different components of the reaction medium can be brought into contact by any technique known to the person skilled in the art, for example by simple mixing of the starting reagents and reactants, optionally in the presence of a solvent, the reaction medium can be homogeneous or heterogeneous. As a variant, the at least one polyene can first be dissolved in the at least one solvent, then the at least one mercapto donor compound is added, and the at least one radical initiator and the at least one acid catalyst are used.

[0048] The reaction is generally carried out at atmospheric pressure, but can also be carried out at reduced pressure, under vacuum or under increased pressure, the pressure can range from atmospheric pressure to 10 MPa (100 bars), preferably from atmospheric pressure to 5 MPa (50 bars), in particular from atmospheric pressure to 2 MPa (20 bars).

[0049] The process according to the application can be carried out at any temperature, preferably at a temperature between 25°C and 150°C, more preferably between 25°C and 100°C, in particular between 25°C and 70°C, the temperature can be easily adapted according to the nature of the reagents, the solvent and the type of catalyst used and the pressure applied to the reaction medium.

[0050] The reaction can take place between a few minutes and a few hours, the duration depending on the operating conditions mentioned above.

[0051] The process of the application is characterized in that the step b / of carrying out the reaction simultaneously comprises an acid-catalyzed mercapto-functionalization of the at least one polyene and a radical mercapto-functionalization of the at least one polyene, the acid-catalyzed mercapto-functionalization and the radical mercapto-functionalization being carried out simultaneously.

[0052] The term "simultaneously" is understood to mean that the acid-catalyzed mercapto-functionalization and the radical mercapto-functionalization are carried out simultaneously and / or alternately and / or sequentially without isolating the intermediates of the reaction, until the at least one polyene is converted, preferably until it is completely converted into a polythiol.

[0053] As mentioned above, the polyene comprises at least two unsaturations in the form of double bonds, so that the two reactions can be carried out simultaneously on the same polyene compound. Indeed, in the example where the polyene comprises two double bonds bearing substituents different from each other, one of the substituents undergoes a radical mercapto-functionalization and the other undergoes an acid-catalyzed mercapto-functionalization.

[0054] When the at least one polyene comprises two double bonds bearing identical substituents (for example in the case of a symmetrical polyene), by acting on the operating conditions, it is also possible to simultaneously carry out a radical mercapto-functionalization reaction and an acid-catalyzed mercapto-functionalization reaction, one on at least one olefinic unsaturation and the other on at least one other olefinic unsaturation.

[0055] The process according to the application can be carried out continuously or batchwise. When the reaction is carried out continuously, step b / advantageously but most often comprises a step of recirculating the reaction medium in a reaction loop.

[0056] The Applicant has found that the simultaneous carrying out of a radical mercapto-functionalization reaction and an acid-catalyzed mercapto-functionalization reaction according to the process of the application surprisingly leads to a complete conversion of the at least one starting polyene, which is generally incomplete when these reactions are carried out separately. By "complete conversion" is understood to mean a conversion degree greater than 90%, more generally greater than 95%, generally greater than 99% and more particularly equal to 100% of the number of double bonds present in the at least one starting polyene.

[0057] The process of the application also allows the preparation of a polythiol having a high content of thiol functions and a limited or even zero content of double bonds. For example, in the case where the starting polyene has 3 double bonds, and in the case where the polyene is completely converted, the polyene will be converted into a mixture of polythiols, each polythiol comprising 3 thiol (-SH) functions.

[0058] The fact of combining a radical route and an acid-catalyzed route makes it possible not only to obtain a polythiol comprising primary and secondary and / or tertiary thiols, but also to obtain a polythiol that is different from the polythiol obtained if the two reactions were carried out separately. This control of the thiol content makes it possible to adjust the reactivity of the polythiol compounds formed, in particular during their use.

[0059] In addition, the process according to the application makes it possible to improve the kinetics of the reaction, thereby causing the formation of side reactions (for example intramolecular reactions) to be minimized and to limit the content of impurities (for example sulfides).

[0060] In addition, it has been observed that the regioselectivity of the mercapto-functionalization reaction can be controlled by the operating conditions in the process of the application. In addition, the adjustment of the operating conditions also makes it possible to control the proportions of polythiol isomers formed.

[0061] The mixture of polythiols obtained is isolated from the reaction medium according to any method known to the person skilled in the art, for example by evaporation or distillation of the solvent under normal or reduced pressure. The mixture of polythiols can be purified by conventional methods well known to the person skilled in the art, for example selected from purification on ion exchange resins, filtration on activated carbon, diatomaceous earth or zeolites, etc.

[0062] The polythiol mixture obtained according to the process of the application can be used as such, or the polythiols of the mixture can be isolated by any separation method well known to the person skilled in the art, such as distillation, crystallization, preparative chromatography, etc.

[0063] The present application also relates to a mixture of at least two polythiols obtainable according to the process described above.

[0064] Thus, the mixture of polythiols obtainable according to the process of the application can find many applications which are very advantageous in many fields, such as, and not limitatively, as:

[0065] • crosslinking agents or vulcanizing agents;

[0066] • reagents for the preparation of sulfur-containing compounds such as thiocarbamates, polysulfides, etc.;

[0067] • chain transfer agents;

[0068] • metal complexing agents;

[0069] • ore flotation agents;

[0070] • antioxidants;

[0071] • heat stabilizers;

[0072] • and the like.

[0073] The present application also relates to the use of the polythiols obtained by the process according to the application, for example as crosslinking agents for the preparation of adhesives, glues, sealants and epoxy resins, acrylate, isocyanate type paints, etc.

[0074] The polythiols obtained by the process according to the application can also be used as reagents in thiol-ene reactions. Indeed, the presence of thiols with variable reactivity makes it possible to modulate the kinetics of the addition reaction of the thiol function with diene groups.

[0075] The polythiols obtained by the process according to the application can also be used for the preparation of thiocarbamates. Indeed, by reacting polythiols whose thiol function content is controlled, thiocarbamate compounds are obtained, the chemical structure and properties of which are different from those obtained with conventional polythiols synthesized by the radical route or by the acid-catalyzed route.

[0076] The polythiols obtained by the process according to the application can also be used as precursors for the synthesis of polysulfides. Indeed, by oxidation with sulfur, polysulfide compounds can be obtained which can be used as additives for lubricants or rubbers. Using the polythiols obtained by the process according to the application, the polysulfides formed offer variable reactivity due to the difference in steric hindrance at the sulfurization bond.

[0077] The polythiols obtained by the process according to the application can act as chain transfer agents during the synthesis of polymers from monomers such as vinyl monomers, conjugated diene monomers, acrylic monomers, methacrylic monomers, and mixtures of two or more of them in any proportion. The reactivity differences according to the type and content of the mercapto groups allow improving the control of the polymerization reaction.

[0078] As another use, the polythiols obtained by the process of the application can also be used as crosslinking agents for natural, artificial or synthetic rubbers, metal complexing agents, ore flotation agents, as oxygen scavengers, as corrosion inhibitors, etc.

[0079] The application is now illustrated by the following examples, without however conferring a limiting character to the application, the scope of which is defined by the following claims.

[0080] Example:

[0081] One embodiment of the process of the application is illustrated by this example, in which a photoinitiator and a source of radiation are used in a photochemical reactor comprising a recirculation loop on which a tubular reactor is installed. Filters located upstream and downstream of the tubular reactor prevent entrainment of the heterogeneous catalyst.

[0082] The reactor also has a heating system that allows heating to the desired temperature. A cooling system located after the tubular reactor on the recirculation loop makes it possible to cool or heat the liquid feed of the photochemical reactor. A pump placed on this recirculation loop makes it possible to vary the liquid flow rate.

[0083] 100 g (0.73 mol) of β-myrcene (from the company DRT) are introduced, dissolved in 1000 g of tetrahydrofuran (Aldrich) and 0.25 g of Irgacure® 651 (Ciba Specialty Chemicals). 5 g of dry Amberlyst® 15 cation exchange resin (Aldrich) are introduced into the tubular reactor.

[0084] Under recirculation (20 l.h -1 ), the reaction medium is then subjected to nitrogen bubbling to remove traces of residual oxygen. 30 molar equivalents of hydrogen sulfide (H2S) are added to the reaction medium. The tubular reactor is then brought to the desired temperature (100°C). Once this temperature is reached, the lamp is then lit. The reaction medium is subjected to UV radiation (wavelength: 355-365 nm, power: 8 watts) for 6 hours at a temperature of 100°C and a constant pressure of 1.5 MPa is adjusted by the addition of hydrogen sulfide.

[0085] The conversion is monitored by analyzing the samples by high-performance (or high-pressure) liquid chromatography.

[0086] After 6 hours, the conversion of the starting polyenes reached 100%. The lamp was switched off and heating of the tubular reactor was stopped. The excess of hydrogen sulphide was then purged into a thermal oxidizer by reducing the pressure of the medium and then stripping with nitrogen. The mixture was then evaporated under vacuum to remove the solvent and then distilled to remove possible impurities, such as sulphide type impurities.

[0087] The distillation mixture thus obtained had a purity greater than 98% expressed by weight of the trithiols formed. The distillation mixture was characterized by NMR, which confirmed that it consisted of polythiols of the following chemical structure:

[0088]

Claims

1. A method for preparing polythiols, the method comprising at least the following steps: a / Preparation of the thiolization reaction medium, including contacting the following substances: -At least one polyene; -At least one free radical initiator; -At least one heterogeneous acid catalyst; -At least one thiol donor compound; -Optionally, at least one solvent; b / Simultaneously perform the free radical thiolation reaction of the at least one polyene and the acid-catalyzed thiolation reaction of the at least one polyene; c / Recycling contains a mixture of at least two polythiols; The at least one heterogeneous acid catalyst is selected from sulfonated resins, and the at least one free radical initiator is selected from 2,2-dimethoxy-1,2-diphenylethyl-1-one.

2. The method of claim 1, wherein the at least one polyene is a compound whose hydrocarbon chain comprises at least two unsaturated groups in the form of double bonds, the chain being linear or cyclic, saturated or unsaturated, and containing or not containing one or more heteroatoms selected from columns 15, 16 and 17 of the periodic table, and may be interrupted or substituted by one or more aromatic groups.

3. The method according to any one of claims 1-2, wherein the at least one polyene is a hydrocarbon compound comprising 2 to 20 double bonds, including terminal values.

4. The method according to any one of claims 1-2, wherein the at least one polyene is selected from triallyl isocyanurate, terpenes and their derivatives, which contain at least two double bonds.

5. The method according to any one of claims 1-2, wherein the at least one thiol donor compound is selected from hydrogen sulfide, thiocarboxylic acids and their precursors, which are used alone or in combination of two or more of them.

6. The method according to any one of claims 1-2, wherein it is carried out in the absence of a solvent.

7. A mixture of at least two polythiols comprising primary thiols and secondary thiols and / or tertiary thiols, obtained by the method according to any one of claims 1 to 6.

8. Use of the mixture according to claim 7 or the mixture obtained by the method of any one of claims 1 to 6, as a crosslinking agent or vulcanizing agent, a reagent for preparing sulfur-containing compounds, a chain transfer agent, a metal complexing agent, an ore flotation agent, an antioxidant, or a heat stabilizer.

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